Tobacco smoke iron: an initiator/promoter of multiple diseases

HIF2α, Hepcidin and their crosstalk as tumour-promoting signalling

Not all aspects of the disruption of iron homeostasis in cancer have been fully elucidated. Iron accumulation in cancer cells is frequent for many solid tumours, and this is often accompanied by the contemporary rise of two key iron regulators, HIF2α and Hepcidin. This scenario is different from what happens under physiological conditions, where Hepcidin parallels systemic iron concentrations while HIF2α levels are inversely associated to Hepcidin. The present review highlights the increasing body of evidence for the pro-tumoral effect of HIF2α and Hepcidin, discusses the possible imbalance in HIF2α, Hepcidin and iron homeostasis during cancer, and explores therapeutic options relying on these pathways as anticancer strategies.

Iron accumulation typifies renal cell carcinoma tumorigenesis but abates with pathological progression, sarcomatoid dedifferentiation, and metastasis

Iron is a potent catalyst of oxidative stress and cellular proliferation implicated in renal cell carcinoma (RCC) tumorigenesis, yet it also drives ferroptosis that suppresses cancer progression and represents a novel therapeutic target for advanced RCC. The von Hippel Lindau (VHL)/hypoxia-inducible factor-α (HIF-α) axis is a major regulator of cellular iron, and its inactivation underlying most clear cell (cc) RCC tumors introduces both iron dependency and ferroptosis susceptibility. Despite the central role for iron in VHL/HIF-α signaling and ferroptosis, RCC iron levels and their dynamics during RCC initiation/progression are poorly defined. Here, we conducted a large-scale investigation into the incidence and prognostic significance of total tissue iron in ccRCC and non-ccRCC patient primary tumor cancer cells, tumor microenvironment (TME), metastases and non-neoplastic kidneys. Prussian Blue staining was performed to detect non-heme iron accumulation in over 1600 needle-core sections across multiple tissue microarrays. We found that RCC had significantly higher iron staining scores compared with other solid cancers and, on average, >40 times higher than adjacent renal epithelium. RCC cell iron levels correlated positively with TME iron levels and inversely with RCC levels of the main iron uptake protein, transferrin receptor 1 (TfR1/TFRC/CD71). Intriguingly, RCC iron levels, including in the TME, decreased significantly with pathologic (size/stage/grade) progression, sarcomatoid dedifferentiation, and metastasis, particularly among patients with ccRCC, despite increasing TfR1 levels, consistent with an increasingly iron-deficient tumor state. Opposite to tumor iron changes, adjacent renal epithelial iron increased significantly with RCC/ccRCC progression, sarcomatoid dedifferentiation, and metastasis. Lower tumor iron and higher renal epithelial iron each predicted significantly shorter ccRCC patient metastasis-free survival. In conclusion, iron accumulation typifies RCC tumors but declines toward a relative iron-deficient tumor state during progression to metastasis, despite precisely opposite dynamics in adjacent renal epithelium. These findings raise questions regarding the historically presumed selective advantage for high iron during all phases of cancer evolution, suggesting instead distinct tissue-specific roles during RCC carcinogenesis and early tumorigenesis versus later progression. Future study is warranted to determine how the relative iron deficiency of advanced RCC contributes to ferroptosis resistance and/or introduces a heightened susceptibility to iron deprivation that might be therapeutically exploitable.

Suppressive effects of iron chelation in clear cell renal cell carcinoma and their dependency on VHL inactivation

Increasing data implicate iron accumulation in tumorigenesis of the kidney, particularly the clear cell renal cell carcinoma (ccRCC) subtype. The von Hippel Lindau (VHL)/hypoxia inducible factor-α (HIF-α) axis is uniquely dysregulated in ccRCC and is a major regulator and regulatory target of iron metabolism, yet the role of iron in ccRCC tumorigenesis and its potential interplay with VHL inactivation remains unclear. We investigated whether ccRCC iron accumulation occurs due to increased cell dependency on iron for growth and survival as a result of VHL inactivation. Free iron levels were compared between four VHL-mutant ccRCC cell lines (786-0, A704, 769-P, RCC4) and two benign renal tubule epithelial cell lines (RPTEC, HRCEp) using the Phen Green SK fluorescent iron stain. Intracellular iron deprivation was achieved using two clinical iron chelator drugs, deferasirox (DFX) and deferoxamine (DFO), and chelator effects were measured on cell line growth, cell cycle phase, apoptosis, HIF-1α and HIF-2α protein levels and HIF-α transcriptional activity based on expression of target genes CA9, OCT4/POU5F1 and PDGFβ/PDGFB. Similar assays were performed in VHL-mutant ccRCC cells with and without ectopic wild-type VHL expression. Baseline free iron levels were significantly higher in ccRCC cell lines than benign renal cell lines. DFX depleted cellular free iron more rapidly than DFO and led to greater growth suppression of ccRCC cell lines (>90% at ~30-150 µM) than benign renal cell lines (~10-50% at up to 250 µM). Similar growth responses were observed using DFO, with the exception that a prolonged treatment duration was necessary to deplete cellular iron adequately for differential growth suppression of the less susceptible A704 ccRCC cell line relative to benign renal cell lines. Apoptosis and G1-phase cell cycle arrest were identified as potential mechanisms of chelator growth suppression based on their induction in ccRCC cell lines but not benign renal cell lines. Iron chelation in ccRCC cells but not benign renal cells suppressed HIF-1α and HIF-2α protein levels and transcriptional activity, and the degree and timing of HIF-2α suppression correlated with the onset of apoptosis. Restoration of wild-type VHL function in ccRCC cells was sufficient to prevent chelator-induced apoptosis and G1 cell cycle arrest, indicating that ccRCC susceptibility to iron deprivation is VHL inactivation-dependent. In conclusion, ccRCC cells are characterized by high free iron levels and a cancer-specific dependency on iron for HIF-α overexpression, cell cycle progression and apoptotic escape. This iron dependency is introduced by VHL inactivation, revealing a novel interplay between VHL/HIF-α dysregulation and ccRCC iron metabolism. Future study is warranted to determine if iron deprivation using chelator drugs provides an effective therapeutic strategy for targeting HIF-2α and suppressing tumor progression in ccRCC patients.

Fractional anisotropy of white matter, disability and blood iron parameters in multiple sclerosis

Multiple sclerosis (MS) is a disorder related to myelin damage, which can be investigated by neuroimaging techniques such as fractional anisotropy (FA), a measure of microstructural white matter properties. The objectives of this study were to investigate (1) the relationship between FA and disability using an extremes of outcome approach, and (2) whether blood iron parameters were associated with FA and/or disability. Patients diagnosed with MS (n = 107; 14 males and 93 females) had iron parameter tests and disability determinations using the Expanded Disability Status Scale (EDSS). FA was recorded in 48 white matter tracts in 11 of the female patients with MS and 12 female controls.

RESULTS

In patients with high disability scores the mean FA was significantly lower (0.34 ± 0.067) than in the control group (0.45 ± 0.036; p = 0.04), while patients with low disability had mean FA values (0.44 ± 0.014) similar to controls (p = 0.5). Positive associations were found between FA and the iron parameters serum iron, ferritin and percentage transferrin saturation (%Tfsat) in all the white matter tracts. For % Tfsat, the associations were highly significant in 14 tracts (p < 0.01; r-values 0.74-0.84) and p < 0.001 (r = 0.83) in the superior fronto occipital fasciculus (LH). In the whole patient group a trend was found towards an inverse association between the EDSS and the %Tfsat (r = -0.26, p = 0.05) after excluding male gender and smoking as confounders, suggesting reduced disability in the presence of higher blood iron parameters. Additionally, significant inverse associations between disease duration and haemoglobin (p = 0.04) as well as %Tfsat (p = 0.02) suggested that patients with MS may experience a decrease in blood iron concentrations over time.

A critical review of assays for hazardous components of air pollution

Increased mortality and diverse morbidities are globally associated with exposure to ambient air pollution (AAP), cigarette smoke (CS), and household air pollution (HAP). The AAP-CS-HAP aerosols present heterogeneous particulate matter (PM) of diverse chemical and physical characteristics. Some epidemiological models have assumed the same health hazards by PM weight for AAP, CS, and HAP regardless of the composition. While others have recognized that biological activities and toxicity will vary with components, we focus particularly on oxidation because of its major role in assay outcomes. Our review of PM assays considers misinterpretations of some chemical measures used for oxidative activity. Overall, there is low consistency across chemical and cell-based assays for oxidative and inflammatory activity. We also note gaps in understanding how much airborne PM of various sizes enter cells and organs. For CS, the body burden per cigarette may be much below current assumptions. Synergies shown for health hazards of AAP and CS suggest crosstalk in detoxification pathways mediated by AHR, NF-κB, and Nrf2. These complex genomic and biochemical interactions frustrate resolution of the toxicity of specific AAP components. We propose further strategies based on targeted gene expression based on cell-type differences.

Transferrin receptor 1 upregulation in primary tumor and downregulation in benign kidney is associated with progression and mortality in renal cell carcinoma patients

The central dysregulated pathway of clear cell (cc) renal cell carcinoma (RCC), the von Hippel Lindau/hypoxia inducible factor-α axis, is a key regulator of intracellular iron levels, however the role of iron uptake in human RCC tumorigenesis and progression remains unknown. We conducted a thorough, large-scale investigation of the expression and prognostic significance of the primary iron uptake protein, transferrin receptor 1 (TfR1/CD71/TFRC), in RCC patients. TfR1 immunohistochemistry was performed in over 1500 cores from 574 renal cell tumor patient tissues (primary tumors, matched benign kidneys, metastases) and non-neoplastic tissues from 36 different body sites. TfR1 levels in RCC tumors, particularly ccRCC, were significantly associated with adverse clinical prognostic features (anemia, lower body mass index, smoking), worse tumor pathology (size, stage, grade, multifocality, sarcomatoid dedifferentiation) and worse survival outcomes, including after adjustments for tumor pathology. Highest TfR1 tissue levels in the non-gravid body were detected in benign renal tubule epithelium. Opposite to TfR1 changes in the primary tumor, TfR1 levels in benign kidney dropped during tumor progression and were inversely associated with worse survival outcomes, independent of tumor pathology. Quantitative measurement of TfR1 subcellular localization in cell lines demonstrated mixed cytoplasmic and membranous expression with increased TfR1 in clusters in ccRCC versus benign renal cell lines. Results of this study support an important role for TfR1 in RCC progression and identify TfR1 as a novel RCC biomarker and therapeutic target.

Partial associations of dietary iron, smoking and intestinal bacteria with colorectal cancer risk

Smoking and high red meat intake have been associated with colorectal cancer (CRC) risk. Increased iron exposure may be a common factor, favoring the colonization of certain bacterial pathogens that preferentially grow in an iron-rich luminal environment. We analyzed the data from a population-based case-control study of CRC and measured antibody levels against flagelin of Salmonella (FliC), one of the irontrophic bacteria, in 2 independent blood collections. The risk of CRC synergistically increased by combined exposures to heme iron intake and pack-yr (PY) of cigarette smoking (P value for the interaction = 0.039 on the continuous scale). There was a marginally significant interaction between heme iron intake and PY in increasing FliC antibody in the U.S. control subjects (P = 0.055), although no iron or smoking data were available for Dutch samples. Furthermore, FliC antibody levels were significantly higher in patients with colorectal polyps and cancer than in controls in both Dutch (3.93 vs. 2.23) (P = 0.014) and U.S. samples (6.65 vs. 4.37) (P < 0.001). Potential roles of iron from cigarette smoking and dietary heme in CRC through altering irontrophic luminal bacterial population may warrant further investigation.

Emerging mechanistic targets in lung injury induced by combustion-generated particles

The mechanism for biological effect following exposure to combustion-generated particles is incompletely defined. The identification of pathways regulating the acute toxicological effects of these particles provides specific targets for therapeutic manipulation in an attempt to impact disease following exposures. Transient receptor potential (TRP) cation channels were identified as "particle sensors" in that their activation was coupled with the initiation of protective responses limiting airway deposition and inflammatory responses, which promote degradation and clearance of the particles. TRPA1, V1, V4, and M8 have a capacity to mediate adverse effects after exposure to combustion-generated particulate matter (PM); relative contributions of each depend upon particle composition, dose, and deposition. Exposure of human bronchial epithelial cells to an organic extract of diesel exhaust particle was followed by TRPV4 mediating Ca(++) influx, increased RAS expression, mitogen-activated protein kinase signaling, and matrix metalloproteinase-1 activation. These novel pathways of biological effect can be targeted by compounds that specifically inhibit critical signaling reactions. In addition to TRPs and calcium biochemistry, humic-like substances (HLS) and cell/tissue iron equilibrium were identified as potential mechanistic targets in lung injury after particle exposure. In respiratory epithelial cells, iron sequestration by HLS in wood smoke particle (WSP) was associated with oxidant generation, cell signaling, transcription factor activation, and release of inflammatory mediators. Similar to WSP, cytotoxic insoluble nanosized spherical particles composed of HLS were isolated from cigarette smoke condensate. Therapies that promote bioelimination of HLS and prevent the disruption of iron homeostasis could function to reduce the harmful effects of combustion-generated PM exposure.

Occupational exposures to aluminum and iron and risk of lung epithelium atypia in sudan

This study investigated the risk of lung cytological atypical changes in regards to occupational exposure to aluminum and iron. Detailed job histories were elicited from 130 incident cases with confirmed exposure to aluminum (50) or iron (80) and 157 population controls (nonexposed). Cytological atypia in sputum (dysplasia) was identified in four cases and none of controls (RR =10.8550; 95% CI = 0.5898 to 199.7815, P = 0.1086), hence, metaplasia was observed among 15 (11.5%) of the cases and 10 (6%) of controls (RR = 1.8115; 95% CI = 0.8424-3.8956; P = 0.1283). Evidences of viral infection were observed in 18 (14%) of the cases and 8 (5%) of controls (RR = 2.7173; 95% CI = 1.2213-6.0460; P = 0.0143). Moniliasis was observed in 28 (22%) of the cases and 19 (12%) of controls (RR = 1.6632; 95% CI = 0.9728-2.8435; P = 0.06). Cross-categorizations of aluminum exposure and iron use suggest greater risk associated with iron exposure than aluminum in these workers.